Remote Detection of Induction Weld Temperature

ABSTRACT

Systems and methods are provided for controlling welding. One embodiment is a method for controlling welding of a composite part. The method includes locating a linear fiber optic sensor along a composite part comprising a matrix of thermoplastic reinforced by fibers, measuring temperatures along the weld line via the linear fiber optic sensor, performing induction welding at the composite part along the weld line, determining a continuum of weld temperatures along the weld line, and controlling the induction welding based on the continuum of weld temperatures.

FIELD

The disclosure relates to the field of composite materials, and inparticular, to fabrication of composite parts.

BACKGROUND

Composite parts each comprise a matrix of material reinforced by fibers.For example, some composite parts are made from layers of unidirectionalcarbon fibers that are stacked in different orientations within athermoplastic matrix. In order to adhere thermoplastic composite partstogether, the parts may be induction welded to form an integralcomposite part. During induction welding, fibers in the composite partsreact to an applied magnetic field, resulting in heating at thecomposite parts. This increases a temperature of a thermoplastic matrixat an interface of the composite parts to a melting temperature. In thisstate, thermoplastic material from the composite parts merges together,and upon cooling, the thermoplastic matrices of the two composite partssolidify into one.

While induction welding provides a substantial benefit over priortechniques, controlling the temperature at which an induction weld isperformed remains a difficult process. This is unfortunate because if aninduction weld is not performed within a specific temperature range, theweld may not be in conformance with desired parameters.

Therefore, it would be desirable to have a method and apparatus thattake into account at least some of the issues discussed above, as wellas other possible issues.

SUMMARY

Embodiments described herein provide systems and methods which utilizeremote sensing technologies to infer a temperature at a weld line forinduction welding thermoplastic composite parts together. Thesetechniques are non-invasive and do not require the placement of sensorsdirectly within the weld interface, which increases weld strength andreduces expense. Furthermore, because the sensors are not directlyplaced at the weld interface, the sensors need not be highly temperatureresistant or sacrificial in nature. Thus, monitoring the weldtemperature with external sensors during the welding process is asubstantial improvement to achieve desired physical properties for aninduction weld.

One embodiment is a method for controlling welding of a composite part.The method includes locating a linear fiber optic sensor along acomposite part comprising a matrix of thermoplastic reinforced byfibers, measuring temperatures along the weld line via the linear fiberoptic sensor, performing induction welding at the composite part alongthe weld line, determining a continuum of weld temperatures along theweld line, and

controlling the induction welding based on the continuum of weldtemperatures.

A further embodiment is a non-transitory computer readable mediumembodying programmed instructions which, when executed by a processor,are operable for performing a method. The method includes locating alinear fiber optic sensor along a composite part comprising a matrix ofthermoplastic reinforced by fibers, measuring temperatures along theweld line via the linear fiber optic sensor, performing inductionwelding at the composite part along the weld line, determining acontinuum of weld temperatures along the weld line, and controlling theinduction welding based on the continuum of weld temperatures.

A further embodiment is an apparatus for facilitating welding of acomposite part. The apparatus includes an end effector that generates anelectromagnetic field which causes a weld line of a composite part togenerate heat resulting in induction welding, a linear fiber opticsensor disposed at the composite part along the weld line, and acontroller that measures temperatures along the weld line via the linearfiber optic sensor, determines a continuum of weld temperatures alongthe weld line, and controls the induction welding based on the continuumof weld temperatures.

Other illustrative embodiments (e.g., methods and computer-readablemedia relating to the foregoing embodiments) may be described below. Thefeatures, functions, and advantages that have been discussed can beachieved independently in various embodiments or may be combined in yetother embodiments further details of which can be seen with reference tothe following description and drawings.

DESCRIPTION OF THE DRAWINGS

Some embodiments of the present disclosure are now described, by way ofexample only, and with reference to the accompanying drawings. The samereference number represents the same element or the same type of elementon all drawings.

FIG. 1 illustrates an induction welding system in an illustrativeembodiment.

FIG. 2 is a flowchart illustrating a method for operating an inductionwelding system in an illustrative embodiment.

FIG. 3 is a flowchart illustrating a further method for operating aninduction welding system in an illustrative embodiment.

FIG. 4 is a perspective view of an induction welding system operating aninduction coil to create an induction weld in an illustrativeembodiment.

FIG. 5 is a top view of an induction welding system operating aninduction coil to create an induction weld in an illustrativeembodiment.

FIG. 6 is an end view of an induction welding system operating aninduction coil to create an induction weld in an illustrativeembodiment.

FIG. 7 is a chart illustrating relationships between induction weldtemperature and heat sink temperature in an illustrative embodiment.

FIG. 8 is a chart illustrating relationships between detected voltageand induction current in an illustrative embodiment.

FIG. 9 is a flowchart illustrating a method for monitoring temperaturevia a linear fiber optic sensor in an illustrative embodiment.

FIG. 10 is a perspective view of linear fiber optic sensors that monitortemperature in an illustrative embodiment.

FIG. 11 is a cut-through view of a linear optic fiber sensor in anillustrative embodiment.

FIG. 12 is a chart depicting a continuum of temperatures measured by alinear fiber optic sensor in an illustrative embodiment.

FIG. 13 is a flow diagram of aircraft production and service methodologyin an illustrative embodiment.

FIG. 14 is a block diagram of an aircraft in an illustrative embodiment.

DESCRIPTION

The figures and the following description provide specific illustrativeembodiments of the disclosure. It will thus be appreciated that thoseskilled in the art will be able to devise various arrangements that,although not explicitly described or shown herein, embody the principlesof the disclosure and are included within the scope of the disclosure.Furthermore, any examples described herein are intended to aid inunderstanding the principles of the disclosure, and are to be construedas being without limitation to such specifically recited examples andconditions. As a result, the disclosure is not limited to the specificembodiments or examples described below, but by the claims and theirequivalents.

FIG. 1 is a block diagram of an induction welding system 100 in anillustrative embodiment. Induction welding system 100 comprises anysystem, device, or component operable to generate magnetic fields whichinductively heat an interface between thermoplastic composite parts inorder to form an induction weld. In this embodiment, induction weldingsystem 100 comprises robot 110, which includes a controller 112 and amemory 114 for managing the operations of a kinematic chain 116comprising actuators 115 and rigid bodies 117. By controlling themotions of kinematic chain 116, the position, speed, and/or direction ofan end effector 118 bearing an induction coil 119 may be adjusted.Controller 112 may further control an amount of current applied toinduction coil 119, in order to increase or decrease a magnetic fieldgenerated by the induction coil 119. This in turn controls a temperatureof a weld interface 130 between laminates 120-121 where inductionwelding is desired. Controller 112 may be implemented, for example, ascustom circuitry, as a hardware processor executing programmedinstructions, or some combination thereof. Controller 112 may furtherdirect the operations of the various components of robot 110 inaccordance with instructions stored in a Numerical Control (NC) programstored in memory 114.

Induction coil 119 generates a magnetic field in response to appliedcurrent. The intensity of the magnetic field that is generated is basedon the amount of current applied. Thus, induction coil 119 may becontrollably adjusted in order to generate magnetic fields of desiredstrength.

Due to the design of induction coil 119, the magnetic fields generatedby induction coil 119 are strongest proximate to weld interface 130between laminates 120-121. In response to experiencing the magneticfield, fibers 124-125 (e.g., carbon fibers) operate as susceptors andgenerate heat. This increases a temperature of thermoplastic 122-123 atthe laminates 120-121, causing the thermoplastic 122-123 to reach aglass transition temperature. At the glass transition temperature,thermoplastic 122 in the laminate 120 melds or welds with thermoplastic123 in the other of the laminates 121. This merges the thermoplastic122-123 in the laminates 120-121 into an integral mass which cools intoa single matrix of thermoplastic. Thermoplastic 122-123 may comprise anysuitable thermoplastic, such as Polyetheretherketone (PEEK),Polyetherketoneketone (PEKK), etc. Mandrel 150 supports laminates duringperformance of the induction weld.

Heat sink 140 is separated from the weld interface 130 at whichinduction welding takes place by one or more of the laminates 120-121.Heat sink 140 absorbs and disperses heat from the surface 132 of thelaminate 120. This ensures that heat generated within the laminate 120at weld interface 130 (e.g., a weld interface of the laminate) does notcause the surface 132 (e.g., a portion of the laminate), to exceed theglass transition temperature (which would result in undesired structuralchanges to the laminate 120 and/or the laminate 121).

In this embodiment, sensor 160 is embedded within heat sink 140, andmeasures temperatures (or voltages indicative of magnetic fieldstrength) at a distance D away from the weld interface 130. However, infurther embodiments, sensor 160 may be placed at a left or right edge ofthe heat sink, or at the left or right edge of the weld interface 130,or beneath the laminate 121. Based on a known relationship betweentemperature at the weld interface 130 and temperature at heat sink 140(or based on a known relationship between measured magnetic fieldstrength and current applied to induction coil 119), a temperature ofthe induction weld performed at the weld interface 130 may bedetermined. Sensor 160 may comprise a thermocouple or an ElectromagneticField (EMF) sensor (e.g., an EMG sensor having a calibrated loop havingat least two hundred loops), such as a sensor designed for operation toacquire measurements at a sampling rate between one and five Megahertz.In further embodiments, sensor 160 comprises an infrared (IR) sensorthat measures temperature.

Illustrative details of the operation of induction welding system 100will be discussed with regard to FIGS. 2-3. Assume, for this embodiment,that multiple thermoplastic laminates have been laid-up and placedagainst each other for the formation of an induction weld that will makethe laminates into a single integral composite part. For example, thismay comprise placing a composite part/laminate in contact with anothercomposite part/laminate prior to initiating the induction welding.

FIG. 2 is a flowchart illustrating a method 200 for operating aninduction welding system based on remotely detected temperatures in anillustrative embodiment. The steps of method 200 are described withreference to induction welding system 100 of FIG. 1, but those skilledin the art will appreciate that method 200 may be performed in othersystems. The steps of the flowcharts described herein are not allinclusive and may include other steps not shown. The steps describedherein may also be performed in an alternative order.

In step 202, controller 112 initiates induction welding along a weldinterface of a composite part (e.g., along weld interface 130 at alaminate 120) comprising a matrix of thermoplastic 122 reinforced byfibers 124. The induction welding is performed along an intersection ofthe laminate 120. Initiating induction welding may comprise applying acurrent to induction coil 119 in order to generate a magnetic field, andmoving the induction coil 119 along a weld line in order to fusethermoplastic from two different laminates along a substantial distance(e.g., several to many feet). In further embodiments, the induction coil119 moves relative to the laminates 120-121, the laminates 120-121 aremoved relative to the induction coil 119, or some combination thereof isperformed.

Welding the composite part/laminate comprises generating heat within thefibers 124 at the composite part/laminate in response to an appliedmagnetic field. The width of the weld line may be substantially smallerthan the length, and may for example be an inch or less, while the weldline may continue for any feasible distance (e.g., hundreds of feet).

In step 204, controller 112 determines a remote temperature of a portionof the composite part (e.g., surface 132) that receives heat from theweld interface (e.g., weld interface 130) via conduction during theinduction welding. That is, controller 112 may consult temperature datafrom sensor 160, which in this embodiment is disposed at heat sink 140,to determine a temperature of surface 132. Surface 132 has beenconductively heated by the fibers 124-125 within the laminates 120-121,which are inductively heated. This heating is controlled by heat sink140 to draw off the heat rising from the fibers 124-125 below and abovethe weld interface 130. The temperature readings may be acquiredconstantly, periodically (e.g., every millisecond, every tenmilliseconds, etc.), or at certain processing checkpoints (e.g., acertain amount of time after end effector 118 moves to a new location).

In step 206, controller 112 determines a welding temperature at the weldinterface of the composite part (e.g., the weld interface 130) based onthe remote temperature during the induction welding. In someembodiments, this determination is made based on known correlationsdetermined from experimental results. For example, controller 112 mayconsult a model (e.g., a linear model or other model) to derive, basedon previously experimentally proven results, a temperature at weldinterface 130 based on input from sensor 160. In one embodiment,inferring the welding temperature is determined based on the remotetemperature as well as a distance between the portion (e.g. surface 132)and the weld interface (e.g., weld interface 130).

Controller 112 may further store this temperature information,correlated with information indication a location of end effector 118along a weld line, for later reporting to a technician. The report maycomprise a graphical or textual series of statements indicating whetheror not the temperature at weld interface 130 was within a desired range.

In further embodiments, controller 112 may control an amount of currentapplied to induction coil 119 in real-time based on the determinedwelding temperature. This enables the controller 112 to control theinduction welding by adjusting a strength of the magnetic field. Forexample, if the welding temperature is below a desired operating rangefor more than a threshold period of time (e.g., several milliseconds),controller 112 may increase the amount of current applied to theinduction coil 119. Alternatively, if the welding temperature is above adesired operating range for more than a threshold period of time (e.g.,several milliseconds), controller 112 may decrease the amount of currentapplied to the induction coil 119. In a further embodiment, controller112 adjusts a speed at which end effector 118 moves along the weldingline, based on the inferred welding temperature. In this manner,controller 112 may control the induction welding based on the weldingtemperature. Controller 112 may further control the rate of theinduction welding along the welding line.

Method 200 provides a substantial advantage over prior techniquesbecause it enables the temperature of an induction weld to be accuratelydetermined via remote sensing devices. Thus, no sensing devices areneeded at the weld interface, which reduces the complexity and cost ofsetting up and performing an induction weld. This also eliminates theneed to add an element at the weld interface 130 for measuring weldtemperature. Such an element would make it more difficult to produce aweld within desired tolerances, and would add weight to the structure.Furthermore, because method 200 enables accurate inference of inductionwelding temperatures along an entire weld line, a technician performingthe method 200 is capable of quickly and efficiently identifyinglocations along the weld line where further inspection may be desired.

FIG. 3 is a flowchart illustrating a method 300 for operating aninduction welding system based on remotely detected voltages indicativeof magnetic field strength in an illustrative embodiment. The steps ofmethod 300 are described with reference to induction welding system 100of FIG. 1, but those skilled in the art will appreciate that method 300may be performed in other systems.

In step 302, controller 112 initiates induction welding along a weldinterface of a first composite part (e.g., along weld interface 130 at alaminate 120) comprising a matrix of thermoplastic 122 reinforced byfibers 124, by operating the induction coil 119. This is performed inorder to join the first composite part with a second composite part(e.g., laminate 121). Initiating induction welding may comprise applyinga current to induction coil 119 in order to generate a magnetic field,and moving the induction coil 119 along a weld line in order to fusethermoplastic from two different laminates along a substantial distance(e.g., having a length several to many feet). The width of the weld linemay be substantially smaller than the length, and may for example be aninch or less.

In step 304, controller 112 determines a measured magnetic fieldstrength at a location distinct from the induction coil 119. (e.g., atsensor 160 within heat sink 140). In one embodiment, this step consistsof controller 112 measuring a Root Mean Squared (RMS) voltage at sensor160, and determining measured magnetic field strength based on a knownrelationship between measured RMS voltage and field strength. Thesereadings may be acquired constantly, periodically (e.g., everymillisecond, every ten milliseconds, etc.), or at certain processingcheckpoints (e.g., a certain amount of time after end effector 118 movesto a new location).

In step 306, controller 112 determines a welding temperature at the weldinterface of the first composite part (e.g., the weld interface 130)based on a difference between the measured magnetic field strength and athreshold magnetic field strength during the induction welding. Energyused to generate the magnetic field at induction coil 119 is absorbed byfibers 124 when the fibers 124 are heated by the magnetic field. Thisreduces a strength of the magnetic field. Thus, the amount that amagnetic field has been reduced from a threshold (such as a baseline orexpected amount of strength if no laminates were absorbing energy fromthe magnetic field at the present amount of current being applied toinduction coil 119 indicates an amount of energy that is being used toheat the weld interface 130. This amount of energy may be experimentallymeasured and correlated with specific temperatures at the weld interface130.

To infer the welding temperature, controller 112 may consult a model(e.g., a linear model or other model) to derive, based on previouslyexperimentally proven results, a temperature at weld interface 130 basedon input from sensor 160. Controller 112 may further store thistemperature information, correlated with information indication alocation of end effector 118 along a weld line, for later reporting to atechnician. The report may comprise a graphical or textual series ofstatements indicating whether or not the temperature at weld interface130 was within a desired range.

In one embodiment, inferring the welding temperature is determined basedon the measured voltage as well as a distance between the portion (e.g.surface 132) and the weld interface (e.g., weld interface 130). In suchan embodiment, determining the welding temperature may comprisecalculating, based on the RMS voltage, a current at induction coil 119,and determining the welding temperature based on the current at theinduction coil. In further embodiments, other parameters are involvedincluding welding speed, heat sink parameters, a number of plies offiber in either laminate, a distance of the coil from the weld line, athickness and type of materials being welded, and etc.

In further embodiments, controller 112 may control an amount of currentapplied to induction coil 119 in real-time based on the determinedwelding temperature. For example, if the welding temperature is below adesired operating range for more than a threshold period of time (e.g.,several milliseconds), controller 112 may increase the amount of currentapplied to the induction coil 119. Alternatively, if the weldingtemperature is above a desired operating range for more than a thresholdperiod of time (e.g., several milliseconds), controller 112 may decreasethe amount of current applied to the induction coil 119 to adjust thestrength of the magnetic field. In a further embodiment, controller 112may adjust a speed at which end effector 118 moves along the weldingline, based on the inferred welding temperature, and identifiesout-of-tolerance locations along the welding line in real-time.

The steps of determining, inferring, and controlling may be performediteratively in a closed loop during induction welding. In this manner,the controller 112 performs closed loop control of an amount of powerapplied during the induction welding, based on a current of theinduction coil 119 and a speed of travel of the end effector 118 along aweld interface of the laminate 120 (i.e., weld interface 130).

Method 300 provides a substantial advantage over prior techniquesbecause it enables the temperature of an induction weld to be accuratelydetermined via remote sensing devices in real time. Thus, no sensingdevices are needed at the weld interface, which reduces the complexityand cost of setting up and performing an induction weld. Furthermore,because method 300 enables accurate inference of induction weldingtemperatures along an entire weld line (i.e., based upon measuredtemperatures during the welding pass), a technician performing themethod 300 is capable of quickly and efficiently identifying locationsalong the weld line where further inspection may be desired, and evenmay identify these locations as they occur.

FIG. 4 is a perspective view of an induction welding system 400operating an induction coil 412 to create an induction weld in anillustrative embodiment. FIG. 4 is not to scale. In FIG. 4, a robot 410translates induction coil 412 along weld direction 414 to generate amagnetic field having a greatest field strength along weld interface 440between laminate 420 and laminate 430. Laminate 430 is laid-up ontomandrel 460, and heat sinks 450 are disposed atop the laminate 420 inorder to diffuse heat. Laminate 420 may be implemented as a wide panel,but is shown at its current narrow dimensions for clarity. In furtherembodiments, the heat sinks 450 extend beyond the welding line tocontrol bonding temperature of the welding line from edge 442 to edge444.

FIG. 5 is a top view of the induction welding system of FIG. 4 operatingan induction coil to create an induction weld in an illustrativeembodiment, and corresponds with view arrows 5 of FIG. 4. In FIG. 5,heat sinks 450 are depicted, as is a weld line (e.g., having a width ofabout one inch and continuing from left to right). FIG. 5 is not toscale, in order to allow for certain features to be more effectivelyillustrated. An array 500 of Sensors 510 (e.g., Type E thermocouples,EMF sensors, etc.) embedded within each heat sink 450 are also depicted.

While these sensors do not physically contact the weld interface 440,they are capable of determining remote temperatures (or RMS voltages)from which a temperature at the weld interface may be inferred.

In one embodiment, while moving an end effector, controller 112identifies a thermocouple in the array that is disposed closest to theend effector or induction coil, and determines the remote temperature byoperating that thermocouple. In a further embodiment, controller 112identifies an EMF sensor in the array that is disposed closest to theend effector or induction coil, and, magnetic field strength via theoperations of the EMF sensor (e.g., based on a determined voltage at theEMF sensor).

In a further embodiment, a sensor and an end effector travel at the samespeed and in the same direction across the composite part during theinduction welding, such that the sensor remains disposed directly belowthe end effector for the duration of the induction welding process.Stated another way, there is a pairing of the EMF sensor and theinduction coil such that even if the induction coil does not move, butrather the weld interface moves, a desired positioning of the coil tothe EMF sensor is maintained.

FIG. 6 is an end view of the induction welding system of FIG. 4operating an induction coil to create an induction weld in anillustrative embodiment, and corresponds with view arrows 6 of FIG. 4.As shown in FIG. 6, sensors 610, 620, and 640 may comprise temperaturesensors capable of reporting remote temperatures to a controller of arobot operating the induction coil 412. Meanwhile, sensors 610, 620,630, 640, 650, and 660 may comprise RMS voltage sensors for determiningmeasured magnetic field strengths, or both thermocouple and magneticfield sensors at all locations. In further embodiments, an inductionwelding system may utilize any or a combination of the sensors depictedin FIG. 6 to infer temperature at the weld interface 440. As shown inFIG. 6, mandrel 460 is pressed against laminate 430 at a force F inorder to ensure that laminate 430 and laminate 420 are sufficientlycompacted to generate an induction weld of desired strength.

FIG. 7 is a chart 700 illustrating relationships between induction weldtemperature and heat sink temperature in an illustrative embodiment.These relationships may be considered during step 206 of method 200discussed above. In FIG. 7, relationships between weld temperature andheat sink temperature are depicted for each of multiple differentmaterials (e.g., thermoplastics, or combinations of thermoplastics andfibers). Each relationship is depicted as a best fit line supported byexperimental data (e.g., line 710, line 720, line 730). Thisrelationship may be used to determine whether or not an induction weldis being performed within a desired operating range 740.

FIG. 8 is a chart 800 illustrating relationships between detectedvoltage and induction current in an illustrative embodiment. Theserelationships may be considered during step 306 of method 300 discussedabove. In FIG. 8, relationships between RMS voltages detected (by asensor) and induction current (applied to an induction coil) are knownfor multiple different scenarios indicating a different amount ofmaterial being heated (e.g., no laminate in line 810, one laminate inline 820, and two laminates in line 830). Each relationship is depictedas a best fit line supported by experimental data. The differencebetween these known scenarios may be used to determine a differencebetween expected and measured magnetic fields, which may indicatewhether or not an induction weld is being performed in a desiredoperating range of temperatures.

In further embodiments, fiber optic sensors are utilized to track anentire continuum of temperatures along a weld line. FIG. 9 is aflowchart illustrating a method 900 for monitoring temperature via alinear fiber optic sensor 1100 (FIG. 11) in an illustrative embodiment.Method 900 enables an entire continuum of temperatures to be acquiredand updated in real-time as an induction weld is performed. Sensingperformed by a linear fiber optic sensor 1100 as discussed herein isbased on Rayleigh Scattering happening inside of the sensor. Thisphenomenon may be observed to determine changes in dimensions of thesensor resulting from a change in temperature. Specifically, changes inmeasured optical frequency may indicate a change in temperature at thesensor.

In step 902, a linear fiber optic sensor 1100 is located at a weld linealong a composite part comprising a matrix of thermoplastic reinforcedby fibers. The linear fiber optic sensor 1100 comprises an elongatedthread that proceeds along an expected weld line. In some embodiments,the weld line follows a contour, and the linear fiber optic sensor 1100is conformed to the contour. The linear fiber optic sensor 1100 includessensing elements which change in length in response to changes intemperature, as well as in response to applied forces. The linear fiberoptic sensor 1100 may further include a cover that shields the elementsof the linear fiber optic sensor 1100 from physical strain whileinduction welding is performed. In one embodiment, the cover is rigidand does not substantially thermally expand during induction welding,which means that the cover does not generate strain that stretches theelements.

In step 904, temperatures are measured along the weld line via thelinear fiber optic sensor 1100. This may comprise measuring referenceoptical frequency shifts for light from a laser traveling from an end ofthe linear fiber optic sensor 1100 to elements within the linear fiberoptic sensor 1100. During this process, a controller operates the laserto transmit the light along the linear fiber optic sensor 1100. At eachelement within the linear fiber optic sensor 1100, a portion of thelaser is reflected back towards the laser. By measuring the opticalfrequency shift for the laser as its light reaches and returns from eachelement, a continuum of baseline, ambient temperature optical frequencyshifts is constructed. In further embodiments, these techniques are alsoused within a fabricated composite part in order to measure change instrain instead of (or together with) changes in temperature. Themeasurements of strain may be utilized to determine stress/loading of ajoint in real time while the composite part is in service.

In step 906, induction welding is performed at the composite part alongthe weld line (which may be parallel to the linear fiber optic sensor1100). During induction welding, the composite part is heated, and thisheat is transferred via conduction to the linear fiber optic sensor1100. The heating of the linear fiber optic sensor results in thermalexpansion of the elements of the fiber optic sensor, which increases thelength of the elements and therefore alters the frequency of light froma laser that traverses the linear fiber optic sensor. These frequencyshifts are measurable, and are capable of being correlated with knowntemperatures.

In step 908, a controller measures weld optical frequency shifts, whichare changes in optical frequency for light from the laser as the lighttravels from the end of the linear fiber optic sensor to the elementswhile the induction welding is being performed. In step 910, thecontroller determines a continuum of weld temperatures along the weldline, for example based on differences between the reference opticalfrequency shifts and the weld optical frequency shifts for the elements.In one embodiment, the controller determines the continuum of weldtemperatures along the weld line by: determining sensor temperaturesalong the linear fiber optic sensor, based on differences between areference optical frequency shift and a weld optical frequency shift foreach of the elements, and determining a weld temperature from eachsensor temperature, based on a known relationship between sensortemperatures and welding temperatures. The known relationship can bebased on a material that the composite part is made from, a thickness ofthe composite part, a fiber orientation within the composite part, and adistance of the linear fiber optic sensor to the weld line. In oneembodiment, determining the continuum of weld temperatures along theweld line comprises determining a weld temperature at each of multiplelocations (e.g., each corresponding with a different element of thelinear fiber optic sensor) that are separated by less than onemillimeter from each other.

In step 912, the controller controls the induction welding, based on thecontinuum of weld temperatures. Controlling the induction weldingcomprises adjusting a speed of an induction coil over the weld line,adjusting an amount of current applied to the induction coil, orperforming other operations to manage measured temperatures at one ormore locations along the continuum.

In further embodiments, the linear fiber optic sensor is disposed withinthe composite part, and is utilized in the composite part to transmitoptical signals for the purpose of inspection or communication. Infurther embodiments, the linear fiber optic sensor is disposed withineither of the fiber reinforced composites being welded together. Thelinear fiber optic sensor therefore becomes an integral fiber within thestructure being welded together. The linear fiber optic sensor is thenused after the weld is completed, in order to monitor the health of thebond joint during operation and maintenance. For example, strainexperienced at the bond joint may be monitored via the linear fiberoptic sensor.

FIG. 10 is a perspective view of linear fiber optic sensors that monitortemperature in an illustrative embodiment. FIG. 10 illustrates thatwithin environment 1000, a linear fiber optic sensor may be disposed atlocations 1040, 1060, and/or 1070 proximate to a weld line 1022 betweena composite part 1010 and a composite part 1020 that is shaped onto amandrel 1030. The linear fiber optic sensor may even be disposed atlocation 1050 within one of the composite parts, or at other locations.These locations include positions disposed to either side of the weldline 1022, above the weld line 1022, or even below the weld line 1022within the mandrel 1030, just above the weld line itself, or in anylocations that a thermocouple could be disposed as discussed above.

FIG. 11 is a cut-through view of a linear optic fiber sensor in anillustrative embodiment, and corresponds with view arrows 11 of FIG. 10.According to FIG. 11, a linear fiber optic sensor 1100 includes a cover1110 (also referred to as a sheathe) that operates as a physical shieldfor elements 1120, protecting the elements 1120 from physical straincaused by external forces. The elements 1120 are optically transparentand each extend for less than a millimeter. Each element 1120 reflects aportion of light 1134 generated by a laser 1130. For example, in thisembodiment reflected portions 1136 are provided back to the laser 1130,and the timing of these reflected portions indicates a distancetraveled. When one of the elements 1120 is heated, its length increasesfrom a baseline length (L) to a greater length (L+Δ). This results in adifference in optical frequency that is detectable. Thus, it is possibleto experimentally determine a temperature at each of the elements 1120,based on the change in optical frequency. The temperature at each of theelements 1120 is correlated with a temperature at a weld line, based ona distance of the element 1120 from the weld line and a type of materialbeing heated.

FIG. 12 is a chart depicting a continuum 1210 of temperatures measuredby a linear fiber optic sensor in an illustrative embodiment. Accordingto FIG. 12, the continuum 1210 is constructed from temperaturesdetermined along a length of the linear fiber optic sensor, and isupdated in real-time. Temperature in a region 1230 has dropped below athreshold level 1220. Based on this information, a controller determinesthat an additional pass of an induction welding coil will be performedat the region 1230. In further embodiments, in addition to or instead ofperforming an additional pass, coil strength is adjusted or coil speedis adjusted to increase an adjust an amount of heat generated at theweld line.

Examples

In the following examples, additional processes, systems, and methodsare described in the context of an induction welding system.

Referring more particularly to the drawings, embodiments of thedisclosure may be described in the context of aircraft manufacturing andservice in method 1300 as shown in FIG. 13 and an aircraft 1302 as shownin FIG. 14. During pre-production, method 1300 may include specificationand design 1304 of the aircraft 1302 and material procurement 1306.During production, component and subassembly manufacturing 1308 andsystem integration 1310 of the aircraft 1302 takes place. Thereafter,the aircraft 1302 may go through certification and delivery 1312 inorder to be placed in service 1314. While in service by a customer, theaircraft 1302 is scheduled for routine work in maintenance and service1316 (which may also include modification, reconfiguration,refurbishment, and so on). Apparatus and methods embodied herein may beemployed during any one or more suitable stages of the production andservice described in method 1300 (e.g., specification and design 1304,material procurement 1306, component and subassembly manufacturing 1308,system integration 1310, certification and delivery 1312, service 1314,maintenance and service 1316) and/or any suitable component of aircraft1302 (e.g., airframe 1318, systems 1320, interior 1322, propulsionsystem 1324, electrical system 1326, hydraulic system 1328,environmental 1330).

Each of the processes of method 1300 may be performed or carried out bya system integrator, a third party, and/or an operator (e.g., acustomer). For the purposes of this description, a system integrator mayinclude without limitation any number of aircraft manufacturers andmajor-system subcontractors; a third party may include withoutlimitation any number of vendors, subcontractors, and suppliers; and anoperator may be an airline, leasing company, military entity, serviceorganization, and so on.

As shown in FIG. 14, the aircraft 1302 produced by method 1300 mayinclude an airframe 1318 with a plurality of systems 1320 and aninterior 1322. Examples of systems 1320 include one or more of apropulsion system 1324, an electrical system 1326, a hydraulic system1328, and an environmental system 1330. Any number of other systems maybe included. Although an aerospace example is shown, the principles ofthe invention may be applied to other industries, such as the automotiveindustry.

As already mentioned above, apparatus and methods embodied herein may beemployed during any one or more of the stages of the production andservice described in method 1300. For example, components orsubassemblies corresponding to component and subassembly manufacturing1308 may be fabricated or manufactured in a manner similar to componentsor subassemblies produced while the aircraft 1302 is in service. Also,one or more apparatus embodiments, method embodiments, or a combinationthereof may be utilized during the subassembly manufacturing 1308 andsystem integration 1310, for example, by substantially expeditingassembly of or reducing the cost of an aircraft 1302. Similarly, one ormore of apparatus embodiments, method embodiments, or a combinationthereof may be utilized while the aircraft 1302 is in service, forexample and without limitation during the maintenance and service 1316.For example, the techniques and systems described herein may be used formaterial procurement 1306, component and subassembly manufacturing 1308,system integration 1310, service 1314, and/or maintenance and service1316, and/or may be used for airframe 1318 and/or interior 1322. Thesetechniques and systems may even be utilized for systems 1320, including,for example, propulsion system 1324, electrical system 1326, hydraulic1328, and/or environmental system 1330.

In one embodiment, a part comprises a portion of airframe 1318, and ismanufactured during component and subassembly manufacturing 1308. Thepart may then be assembled into an aircraft in system integration 1310,and then be utilized in service 1314 until wear renders the partunusable. Then, in maintenance and service 1316, the part may bediscarded and replaced with a newly manufactured part. Inventivecomponents and methods may be utilized throughout component andsubassembly manufacturing 1308 in order to manufacture new parts.

Any of the various control elements (e.g., electrical or electroniccomponents) shown in the figures or described herein may be implementedas hardware, a processor implementing software, a processor implementingfirmware, or some combination of these. For example, an element may beimplemented as dedicated hardware. Dedicated hardware elements may bereferred to as “processors”, “controllers”, or some similar terminology.When provided by a processor, the functions may be provided by a singlededicated processor, by a single shared processor, or by a plurality ofindividual processors, some of which may be shared. Moreover, explicituse of the term “processor” or “controller” should not be construed torefer exclusively to hardware capable of executing software, and mayimplicitly include, without limitation, digital signal processor (DSP)hardware, a network processor, application specific integrated circuit(ASIC) or other circuitry, field programmable gate array (FPGA), readonly memory (ROM) for storing software, random access memory (RAM),non-volatile storage, logic, or some other physical hardware componentor module.

Also, a control element may be implemented as instructions executable bya processor or a computer to perform the functions of the element. Someexamples of instructions are software, program code, and firmware. Theinstructions are operational when executed by the processor to directthe processor to perform the functions of the element. The instructionsmay be stored on storage devices that are readable by the processor.Some examples of the storage devices are digital or solid-statememories, magnetic storage media such as a magnetic disks and magnetictapes, hard drives, or optically readable digital data storage media.

Although specific embodiments are described herein, the scope of thedisclosure is not limited to those specific embodiments. The scope ofthe disclosure is defined by the following claims and any equivalentsthereof.

For reasons of completeness, various aspects of the invention are setout in the following numbered clauses:

Clause 1. A method for controlling welding of a composite part, themethod comprising: locating a linear fiber optic sensor along acomposite part comprising a matrix of thermoplastic reinforced byfibers;measuring temperatures along the weld line via the linear fiber opticsensor;

-   -   performing induction welding at the composite part along the        weld line;    -   determining a continuum of weld temperatures along the weld        line; and    -   controlling the induction welding based on the continuum of weld        temperatures.        Clause 2. The method of clause 1 wherein:    -   measuring the temperatures comprises measuring reference optical        frequency shifts for a laser travelling from an end of the        linear fiber optic sensor to elements within the linear fiber        optic sensor before the induction welding is performed.        Clause 3. The method of any of clauses 1 or 2 wherein:    -   the weld line is parallel to the linear fiber optic sensor.        Clause 4. The method of any of clauses 1 to 3 further        comprising:    -   measuring the temperatures comprises measuring weld optical        frequency shifts for a laser travelling from an end of the        linear fiber optic sensor to elements within the linear fiber        optic sensor while the induction welding is being performed.        Clause 5. The method of clause 4 wherein:        measuring temperatures is based on differences between reference        optical frequency shifts and weld optical frequency shifts for        elements of the linear fiber optic sensor.        Clause 6. The method of any of clauses 1 to 5 wherein:    -   determining the continuum of weld temperatures along the weld        line comprises determining a weld temperature at each of        multiple locations that are separated by less than one        millimeter from each other.        Clause 7. The method of any of clauses 1 to 6 further        comprising:    -   shielding elements of the linear fiber optic sensor from        physical strain while performing the induction welding.        Clause 8. The method of any of clauses 1 to 7 wherein:    -   the weld line follows a contour, and the method further        comprises conforming the linear fiber optic sensor to the        contour.        Clause 9. The method of any of clauses 1 to 8 wherein:        determining the continuum of weld temperatures along the weld        line comprises:    -   determining sensor temperatures along the linear fiber optic        sensor, based on differences between a reference optical        frequency shift and a weld optical frequency shift for each of        multiple elements of the linear fiber optic sensor; and        determining a weld temperature from each sensor temperature,        based on a known relationship between sensor temperatures and        welding temperatures.        Clause 10. The method of clause 9 wherein:    -   the known relationship is based on a material that the composite        part is made from, a thickness, a fiber orientation, and a        distance of the linear fiber optic sensor to the weld line.        Clause 11. The method of any of clauses 1 to 10 wherein:    -   the linear fiber optic sensor is disposed within the composite        part.        Clause 12. A portion of an aircraft assembled according to the        method of any of clauses 1 to 11.        Clause 13. A non-transitory computer readable medium embodying        programmed instructions which, when executed by a processor, are        operable for performing a method for controlling welding of a        composite part, the method comprising:        locating a linear fiber optic sensor along a composite part        comprising a matrix of thermoplastic reinforced by fibers;        measuring temperatures along the weld line via the linear fiber        optic sensor;    -   performing induction welding at the composite part along the        weld line;    -   determining a continuum of weld temperatures along the weld        line; and    -   controlling the induction welding based on the continuum of weld        temperatures.        Clause 14. The medium of clause 13 wherein:    -   measuring the temperatures comprises measuring reference optical        frequency shifts for a laser travelling from an end of the        linear fiber optic sensor to elements within the linear fiber        optic sensor before the induction welding is performed.        Clause 15. The medium of clause 13 or 14 wherein:    -   the weld line is parallel to the linear fiber optic sensor.        Clause 16. The medium of any of clauses 13 to 15 wherein the        method further comprises:    -   measuring the temperatures comprises measuring weld optical        frequency shifts for a laser travelling from an end of the        linear fiber optic sensor to elements within the linear fiber        optic sensor while the induction welding is being performed.        Clause 17. The medium of clause 16 wherein:        measuring temperatures is based on differences between reference        optical frequency shifts and the weld optical frequency shifts        for the elements.        Clause 18. The medium of any of clauses 13 to 17 wherein:    -   determining the continuum of weld temperatures along the weld        line comprises determining a weld temperature at each of        multiple locations that are separated by less than one        millimeter from each other.        Clause 19. The medium of any of clauses 13 to 18 wherein the        method further comprises: shielding the elements of the linear        fiber optic sensor from physical strain while performing the        induction welding.        Clause 20. The medium of any of clauses 13 to 19 wherein:    -   the weld line follows a contour, and the method further        comprises conforming the linear fiber optic sensor to the        contour.        Clause 21. The medium of any of clauses 13 to 21 wherein:        determining the continuum of weld temperatures along the weld        line comprises:    -   determining sensor temperatures along the linear fiber optic        sensor, based on differences between a reference optical        frequency shift and a weld optical frequency shift for each of        multiple elements of the linear fiber optic sensor; and    -   determining a weld temperature from each sensor temperature,        based on a known relationship between sensor temperatures and        welding temperatures.        Clause 22. The medium of clause 21 wherein:    -   the known relationship is based on a material that the composite        part is made from, a thickness, a fiber orientation, and a        distance of the linear fiber optic sensor to the weld line.        Clause 23. The medium of any of clauses 13 to 22 wherein:    -   the linear fiber optic sensor is disposed within the composite        part.        Clause 24. A portion of an aircraft assembled according to the        method defined by the instructions stored on the computer        readable medium of any of clauses 13 to 23.        Clause 25. An apparatus for facilitating welding of a composite        part, the apparatus comprising:    -   an end effector that generates an electromagnetic field which        causes a weld line of a composite part to generate heat        resulting in induction welding;        a linear fiber optic sensor disposed at the composite part along        the weld line; and        a controller that measures temperatures along the weld line via        the linear fiber optic sensor, determines a continuum of weld        temperatures along the weld line, and controls the induction        welding based on the continuum of weld temperatures.        Clause 26. The apparatus of clause 25 wherein:    -   the controller measures temperatures by measuring reference        optical frequency shifts for a laser to travel from an end of        the linear fiber optic sensor to elements within the linear        fiber optic sensor prior to induction welding, and measuring        weld optical frequency shifts for the laser to travel from the        end of the linear fiber optic sensor to the elements while the        induction welding is being performed.        Clause 27. The apparatus of clause 26 wherein:    -   the continuum of temperatures is based on differences between        reference optical frequency shifts and weld optical frequency        shifts for elements in the linear fiber optic sensor.        Clause 28. The apparatus of any of clauses 25 to 27 wherein:    -   the controller determines the continuum of weld temperatures        along the weld line by determining a weld temperature at each of        multiple locations that are separated by less than one        millimeter from each other.        Clause 29. The apparatus of any of clauses 25 to 28 further        comprising:        a cover that surrounds and shields elements of the linear fiber        optic sensor from physical strain during the induction welding.        Clause 30. The apparatus of any of clauses 25 to 29 wherein:    -   the weld line follows a contour, and the linear fiber optic        sensor conforms to the contour.        Clause 31. The apparatus of any of clauses 25 to 30 wherein:        the controller determines the continuum of weld temperatures        along the weld line by: determining sensor temperatures along        the linear fiber optic sensor, based on differences between a        reference optical frequency shift and a weld optical frequency        shift for each of multiple elements of the linear fiber optic        sensor, and determining a weld temperature from each sensor        temperature, based on a known relationship between sensor        temperatures and welding temperatures.        Clause 32. The apparatus of any of clauses 25 to 31 wherein:    -   the linear fiber optic sensor is disposed within the composite        part.        Clause 33. Fabricating a portion of an aircraft using the        apparatus of any of clauses 25 to 32.        Clause 34. A method for controlling welding of a composite part,        the method comprising: locating a linear fiber optic sensor        along a composite part comprising a matrix of thermoplastic        reinforced by fibers;        measuring reference optical frequency shifts for a laser        travelling from an end of the linear fiber optic sensor to        elements within the linear fiber optic sensor before induction        welding;    -   performing induction welding at the composite part along the        weld line;        measuring reference optical frequency shifts for a laser        travelling from an end of the linear fiber optic sensor to        elements within the linear fiber optic sensor during induction        welding; and    -   controlling the induction welding based on the measured        reference optical frequency shifts before and during induction        welding.        Clause 35. The method of clause 34 wherein:    -   determining a continuum of weld temperatures during induction        welding based on the measured reference optical frequency shifts        before and during induction welding.        Clause 36. The method of any of clause 34 wherein:    -   induction welding along a line parallel to the linear fiber        optic sensor.        Clause 37. The method of any of clause 34 further comprising:    -   shielding elements of the linear fiber optic sensor from        physical strain while performing the induction welding.        Clause 38. The method of any of clause 34 wherein:        determining the continuum of weld temperatures along the weld        line comprises:    -   determining sensor temperatures along the linear fiber optic        sensor, based on differences between a reference optical        frequency shift and a weld optical frequency shift for each of        multiple elements of the linear fiber optic sensor; and    -   determining a weld temperature from each sensor temperature,        based on a known relationship between sensor temperatures and        welding temperatures.

What is claimed is:
 1. A method for controlling welding of a compositepart, the method comprising: locating a linear fiber optic sensor alonga composite part comprising a matrix of thermoplastic reinforced byfibers; measuring temperatures along the weld line via the linear fiberoptic sensor; performing induction welding at the composite part alongthe weld line; determining a continuum of weld temperatures along theweld line; and controlling the induction welding based on the continuumof weld temperatures.
 2. The method of claim 1 wherein: measuring thetemperatures comprises measuring reference optical frequency shifts fora laser travelling from an end of the linear fiber optic sensor toelements within the linear fiber optic sensor before the inductionwelding is performed.
 3. The method of any of claim 1 wherein: inductionwelding along a line parallel to the linear fiber optic sensor.
 4. Themethod of any of claim 1 further comprising: measuring the temperaturescomprises measuring weld optical frequency shifts for a laser travellingfrom an end of the linear fiber optic sensor to elements within thelinear fiber optic sensor while the induction welding is beingperformed.
 5. The method of claim 4 wherein: measuring temperatures isbased on differences between reference optical frequency shifts and weldoptical frequency shifts for elements of the linear fiber optic sensor.6. The method of any of claim 1 wherein: determining the continuum ofweld temperatures along the weld line comprises determining a weldtemperature at each of multiple locations that are separated by lessthan one millimeter from each other.
 7. The method of any of claim 1further comprising: shielding elements of the linear fiber optic sensorfrom physical strain while performing the induction welding.
 8. Themethod of any of claim 1 wherein: determining the continuum of weldtemperatures along the weld line comprises: determining sensortemperatures along the linear fiber optic sensor, based on differencesbetween a reference optical frequency shift and a weld optical frequencyshift for each of multiple elements of the linear fiber optic sensor;and determining a weld temperature from each sensor temperature, basedon a known relationship between sensor temperatures and weldingtemperatures.
 9. The method of claim 8 wherein: the known relationshipis based on a material that the composite part is made from, athickness, a fiber orientation, and a distance of the linear fiber opticsensor to the weld line.
 10. The method of any of claim 1 wherein: thelinear fiber optic sensor is disposed within the composite part.
 11. Aportion of an aircraft assembled according to the method of claim
 1. 12.An apparatus for facilitating welding of a composite part, the apparatuscomprising: an end effector that generates an electromagnetic fieldwhich causes a weld line of a composite part to generate heat resultingin induction welding; a linear fiber optic sensor disposed at thecomposite part along the weld line; and a controller that measurestemperatures along the weld line via the linear fiber optic sensor,determines a continuum of weld temperatures along the weld line, andcontrols the induction welding based on the continuum of weldtemperatures.
 13. The apparatus of claim 12 wherein: the controllerdetermines the continuum of weld temperatures along the weld line bydetermining a weld temperature at each of multiple locations that areseparated by less than one millimeter from each other.
 14. The apparatusof any of claim 12 further comprising: a cover that surrounds andshields elements of the linear fiber optic sensor from physical strainduring the induction welding.
 15. The apparatus of any of claim 12wherein: the weld line follows a contour, and the linear fiber opticsensor conforms to the contour.
 16. The apparatus of any of claim 12wherein: the linear fiber optic sensor is disposed within the compositepart.
 17. A method for controlling welding of a composite part, themethod comprising: locating a linear fiber optic sensor along acomposite part comprising a matrix of thermoplastic reinforced byfibers; measuring reference optical frequency shifts for a lasertravelling from an end of the linear fiber optic sensor to elementswithin the linear fiber optic sensor before induction welding;performing induction welding at the composite part along the weld line;measuring reference optical frequency shifts for a laser travelling froman end of the linear fiber optic sensor to elements within the linearfiber optic sensor during induction welding; and controlling theinduction welding based on the measured reference optical frequencyshifts before and during induction welding.
 18. The method of claim 17wherein: determining a continuum of weld temperatures during inductionwelding based on the measured reference optical frequency shifts beforeand during induction welding.
 19. The method of any of claim 17 wherein:induction welding along a line parallel to the linear fiber opticsensor.
 20. The method of any of claim 17 further comprising: shieldingelements of the linear fiber optic sensor from physical strain whileperforming the induction welding.
 21. The method of any of claim 17wherein: determining the continuum of weld temperatures along the weldline comprises: determining sensor temperatures along the linear fiberoptic sensor, based on differences between a reference optical frequencyshift and a weld optical frequency shift for each of multiple elementsof the linear fiber optic sensor; and determining a weld temperaturefrom each sensor temperature, based on a known relationship betweensensor temperatures and welding temperatures.